Male hypogonadism is a serious condition affecting mostly aging men. The common reasons for hypogonadism in men could be physiological abnormality involving among other factors, improper functioning or growth of the gonads and/or the pituitary-hypothalamus regulatory systems, and aging. Many of the abnormalities that are identified to be commonly associated with the low or decreased testosterone levels include impaired sexual function and/or libido, metabolic syndrome which may be a combination of abdominal obesity, high blood pressure, insulin resistance, lipid disorders; high risk of cardiovascular diseases; reduced bone mass/mineral density and muscle weakness and or degeneration affecting the musculoskeletal system. Other effects of low testosterone levels include negative changes in body composition, depression and other psychological disorders. The average human male produces 4-7 mg of testosterone per day in a circadian pattern, with maximal plasma levels attained in early morning and minimal levels in the evening. It is generally recognized that in a normal adult man of age 17 to 54 years, the serum total testosterone (T) is between about 300 ng/dL to about 1100 ng/dL and this range is referred to as the eugonadal range. Restoration of testosterone levels to the eugonadal range typically corrects many of the cited clinical abnormalities associated with hypogonadism or low testosterone levels.
While oral administration is the most preferred and patient friendly route for administration, the effective oral delivery of testosterone as testosterone and its esters remains a challenge. This is due to extremely poor bioavailability of testosterone, which requires very high dosing as well as frequent dosing due to the short serum half-life. These problems with orally administered testosterone products are primarily due to first pass metabolism. Further, direct oral delivery of testosterone has also been known to cause enzyme induction resulting in potential drug-drug interactions.
Currently, modified testosterones, in form of a methyl analogue of testosterone, and as an undecanoate ester, testosterone undecanoate (TU) are available for oral administration for patients in need of testosterone therapy. However, liver damage including cholestasis, peliosis hepatitis, nodular regenerative hyperplasia, and primary hepatic tumors has been reported with use of methyl testosterone. Testosterone undecanoate is a prodrug which gets converted to testosterone in vivo. Testosterone undecanoate containing products are available in some countries as liquid filled soft-gelatin capsule containing 40 mg of fully solubilized testosterone undecanoate. Testosterone undecanoate is extremely lipophilic (calculated logP of ˜6.5) with a water solubility of <0.3 ng/ml and a melting point around 62° C. It is generally believed that in order to promote lymphatic absorption for better safety profile and to facilitate effective oral delivery of testosterone undecanoate, the testosterone undecanoate must be presented in a bioacceptable solubilizer. Accordingly, research continues into the development of testosterone oral delivery products that can have high drug load and provide for practical unit oral dosage forms.